1,721,051 research outputs found
'Where' and 'what' in the whisker sensorimotor system (Nature Reviews Neuroscience (2008) 9, (601-612))
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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Imaging, Construction, and Analysis of Whole Mouse Brain Vascular Connectome
No full textThe vascular system maintains brain homeostasis optimized for the dynamic computation of neurons. The architecture of the vascular network is fundamental to its functionality as a vital transport system. Nonetheless, comprehensive studies into the structure of the entire brain vascular network and its role in homeostatic regulation have been limited, largely due to the multiscale complexity of the system. This thesis presents novel experimental and computational methodologies developed to construct and analyze mouse brain vascular connectome. We developed techniques to completely label and image whole mouse brain vasculature at sub-micrometer resolution. An efficient computational pipeline was developed to convert immense raw data into a microvascular connectome, the spatial graph representation of the network documenting the position and radius of 6 million interconnected vessel segments in a trillion-voxel space, with 99.9% connectivity accuracy. Utilizing this dataset, we analyzed the structure of the vascular network across brain regions. Topological analyses reveal a common network connection pattern across the brain, leading to a universal structural robustness rooted in percolation transition. Systematic quantification of network orientation preference reveals brain regions with striking microvascular anisotropy, which bears implications for interpreting functional magnetic resonant imaging (fMRI) data. By combining biophysical analysis with numerical simulations, we deduced a formula connecting resting-state metabolism rate to network density and further predicted a common value of maximum tissue oxygen tension across the brain. Extending beyond static structure, perturbation analyses quantified the impacts of single vessel dilation, constriction, and obstruction on local blood flow and tissue oxygenation. Toward constructing vascular connectomes suitable for large-scale flow simulations, we further explored the use of nonlinear optical techniques to image the entire brain vasculature within the cranium at sub-micrometer resolution. High-resolution two-photon and second-harmonic imaging were combined with online processing to define ablation trajectories and parameters for different tissues. Spatiotemporally focused femtosecond pulses were applied for precise and efficient material removal. This entire process was automated through custom-built control software to ensure reliable multi-day operation. This system enabled a detailed examination of the complex vascular connection between the brain and the skull, vital for modeling cerebral blood flow
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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Volitional control of neuromodulation
Full text linkNeuromodulatory neurons release neurotransmitters extrasynaptically to modulate large groups of neurons. Although much work has been done to understand neuromodulation, this has been primarily measured indirectly via action potentials recorded electrically from neuromodulatory somata. In this work, we use genetically modified CNiFER cells, a technique developed in the Kleinfeld lab, to directly measure changes in neuromodulator concentration in real-time. We focus our investigation primarily on cortical noradrenaline, dopamine and acetylcholine, for which CNiFER cells have already been developed. We ask whether spontaneous neuromodulator release occurs in cortex of mice. We find that, indeed, spontaneous dopamine, noradrenaline, and acetylcholine transients occur in cortex of mice. Furthermore, we use real-time feedback of cortical neuromodulation and reinforcement to show that mice can volitionally increase cortical dopamine and noradrenaline levels. We show that mice are able to volitionally link spontaneous dopamine transients to future reward
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Cortex drives orofacial behaviors through distinct brainstem networks
Full text linkFocal activation of motor cortex has been shown to enact behaviorally meaningful motor output. These include defensive behaviors, ethological limb movements, and chewing. Yet the details of how the cortical circuitry interfaces with the brainstem premotor circuits is unknown. We studied the hierarchical nature of this control with respect to orofacial motor acts that involve the vibrissae, jaw, and forelimb. The spinal trigeminal nucleus pars oralis (SpVO) and interpolaris rostralis (SpVIr) contain premotor neurons known to directly synapse on vibrissa, jaw, and forelimb motoneurons. In addition to cortical input, SpVO and SpVIr receive direct sensory signals from the periphery. Their ability to integrate descending motor input and peripheral sensory information positions them as ideal candidates to delimit the specificity of cortex-to-brainstem-to-muscle feed forward networks. Here we show that two distinct clusters of premotor neurons, one in SpVO and a second in SpVIr, control partially overlapping sets of motor actions. We used a transectional virus strategy to encode a red-shifted channelrhodopsin (ChR) in SpVO- and SpVIr-projecting motor cortex neurons. Activation of these two different cortical populations evokes distinct muscle activation during long stimuli. Similar stimulations of localized regions of motor cortex in Thy1-ChR mice show patterns of muscle activity and forelimb and jaw movements that correspond to behaviorally meaningful movements. All together, our data illustrates the functional specificity of motor circuits that originate in cortex and descend onto specific premotor populations. We suggest that the specificity of projections from neurons in motor cortex to premotor nuclei is a major determinate in the coordination of motor actions into behavior
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